EXCITATION OF ALLOWED TRANSITIONS IN ION--ION COLLISIONS
M. McKeown and R. H. G. Reid, 
Department of Applied Mathematics and Theoretical Physics, 
 Queen's University, Belfast BT7 1NN, UK
It is demonstrated that a commonly-used low-energy first-order
approximation is not valid for the calculation of cross sections 
for excitation of allowed transitions in ion--ion collisions. 
Results are given for proton-impact excitation of the  
2s-2p transition in C IV.